1. Field of the Invention
This invention relates to the field of maintaining the integrity of and detecting leaks in fluid systems containing valves. Specifically, the invention relates to a threaded valve plug containing a fluid expansion channel, hereinafter referred to as a "valve plug".
2. Description of the Prior Art
A variety of devices have been used to seal off open-ended valves in fluid systems, thereby preventing the escape or leakage of system fluid into the environment. These devices include blind flanges, caps, and valve plugs, hereinafter referred to as "mechanical devices".
In many cases, these mechanical devices serve as redundant flow barriers or sealing mechanisms to other system components, such as valves, located upstream of these mechanical devices. In these cases, it is often desirable to ascertain whether any components upstream of the mechanical devices are leaking.
With many conventional valve plugs or caps, the plug or cap must be almost totally unscrewed to ascertain whether there is system leakage. In a pressurized fluid system, leakage can result in a pressure buildup on the front face of the valve plug. In such a case, unscrewing the valve plug or cap almost all the way can result in a pressurized expulsion of the mechanical device and an escape of system fluid ("a blowdown") through the open end of the valve which was sealed by the valve plug or cap. Such an expulsion of the mechanical device, the system fluid, or both, can result in human injury, environmental pollution, the disruption of operations associated with the fluid system, and/or fines imposed upon the owner or operator of the fluid system by government regulatory agencies. Fines may also be imposed by regulatory agencies for not having a plug or cap installed in a valve.
Many prior art valve plugs and valve caps do not provide a mechanism to ascertain whether there is fluid system leakage while simultaneously maintaining sufficient thread contact to prevent a blowdown.
Valve plugs are also used in applications where corrosive fluids are present. In such applications, it is undesirable for the valve plug to comprise rubber or other polymer-based members such as O rings. O rings eventually wear out and are particularly susceptible to deterioration in caustic or high temperature environments. Mechanical devices of the prior art such as those disclosed in U.S. Pat. Nos. 4,986,502 to Ceroke, 3,578,285 to Carlton, and 4,470,577 to Warwick disclose the use of O rings or similar sealing members. These sealing members are subject to the deterioration described above. In these devices, the sealing member, rather than the threads, provides the fluid tight seal.
Reliance upon the O ring to provide the fluid tight seal can result in leakage as well as a release of pressurized fluid when the O ring deteriorates or fails. This presents a danger of injury to workers in plants where such valve plugs are installed, as well as an environmental health hazard posed by the release of environmentally hazardous fluids.
The present invention overcomes these problems of prior art mechanical devices by not relying upon O rings or similar types of sealing members in order to form a fluid tight seal with the fluid system in which it is installed. Instead, the present invention utilizes the threads on the cylindrical body of the valve plug to form a fluid tight seal. As shown in FIGS. 1-5, the threads extend around the outer circumference of the cylindrical body. When the valve plug is completely inserted, the resulting fluid tight seal provides sufficient system integrity to prevent a blowdown in systems with pressures of less than or equal to 6,000 psi. As shown in FIG. 4, such insertion is accomplished by completely threading the valve plug into the fluid system.
The present invention is also intended for use in fluid systems where small particulate matter such as rust, grit, sludge, precipitate matter or sandblasting residue is suspended in the fluid. Prior art devices employing (1) long axial channels and/or (2) fluid flow paths with bends or turns, are unacceptable in fluid systems containing solid particulate matter because the small solid particles may either restrict the flow path or totally clog it. Such restriction or clogging will hinder the ability of these devices to indicate system leakage when partially unscrewed.
The present invention overcomes this problem by using a shallow fluid expansion channel centrally located in its face. This design is far less susceptible to the clogging or flow restriction problems of the prior art designs employing long axial channels and/or expansion channels with bends or turns.